1. Field of the Invention
The device and method of this invention reside in the field of railroad warning systems for train operators, railroad personnel and others working in the vicinity of railroad tracks to give train operators warning of railroad personnel near the train tracks and to give train workers, railroad personnel and others warning of oncoming trains, and more particularly relate to a portable train detector and method of detecting a train on a train track.
2. Description of the Prior Art
In the fields of light rail vehicles, trolley lines, third rail-powered vehicles and tramways, alerting work crews or railroad personnel on or near the tracks of an oncoming train or vehicle, herein referred to as a “train,” has been addressed by many methods. Since working on tracks can involve work methods such as digging, hammering and other loud-noise producing acts, workers frequently cannot hear oncoming trains and are in great danger of being struck by such oncoming trains. Also, when individuals, such as first responders, police, firemen, EMS personnel, and track inspectors are on the tracks responding to an emergency or incident, they also are in danger of being struck by such oncoming trains. One of the oldest warning methods employs flag men or whistle men who are positioned a distance away from the workers, such as 3,000 ft., 2,000 ft. or a distance related to the stopping distance of a train from a work crew, in both directions of the track who signal with their flags and/or their whistles to warn of oncoming trains. Due to lack of worker attention or distracting ambient noise, work crews sometimes do not see a flag waving or hear a whistle blowing so that these warning methods can often not be reliable. Further, none of the previous or current warning systems gives an early alert to first responders, police, firemen, track walkers, track work gangs, and track inspectors that a train is approaching.
More recently the train operator can receive warnings by radio that workers are on the tracks in the train's vicinity, but frequently because of poor radio reception in tunnels and track curves and because trains require long distances to stop, such warnings can be ineffective.
Many patents have issued on railroad personnel warning devices, such as U.S. Pat. No. 3,167,282 to S. R. Hursh et. al., which teaches a railroad warning system for warning a work gang working on a railroad track of an approaching train by means of using a train detector physically connected to the track which is activated by having an electrical circuit completed by the pressure of the train's wheels passing thereover. When activated, the device sends a signal to radio receivers and also sets off an audible alarm while at the same time notifying the train operator that a work gang is on the track ahead. This type of system has been improved upon, such as in U.S. Pat. No. 5,924,651 to Penza et. al. where a train transmitter is coupled to a loop buried permanently underneath railroad tracks. Once the train passes over the loop, the warning radio frequency signal can be directed to receivers worn by at least one of the workers in proximity to the railroad tracks to warn such workers of an approaching train in sufficient time for the workers to move away from the tracks. Since many workers can wear the portable radio frequency receivers, they do not need to rely upon others nearby to give them notice of the approach of a train. Such pager-like systems can include vibratory alarms which help to notify workers in loud-noise work zones. The Penza warning system not only can include portable receivers such as portable paging devices, but also can generate an output signal to activate a visual display, such as flashing lights and the like. The Penza system can utilize a control base positioned near the workers, which base can also receive a signal from a transmitter that is installed within the train or such transmitter can be coupled to a loop buried underneath the railroad tracks to sense when the train is passing by and can send a warning signal in sufficient time for the workers to clear the tracks. The use of a loop buried underneath the track or of a pressure transducer positioned on the track to detect the presence of a train or any metal object near the track fails to provide information about the direction and speed of a train on the track. Further, detectors using the interruption of electromagnetic fields are not a consistent means of detecting single track objects as an electromagnetic field can propagate between 8-10 feet and can possibly detect trains on adjacent tracks. Thus they are not single track specific. A further disadvantage in using permanent electromagnetic field sensing devices is that they are susceptible to theft since they are only activated by the presence of large metallic objects, such as trains. Thus there is no warning if such devices are removed.
U.S. Pat. No. 6,471,162 to Pace teaches a system that can be controlled and positioned by workers on the tracks near where they are working to give them advanced notice of an oncoming train. In Pace a train detector probe can be placed near the train tracks at a predetermined distance from the work crew which train detector probe detects an oncoming train by electromagnetic probes which detect changes in the nearby electromagnetic field from the presence of a metallic object and transmit a radio frequency signal to a receiver in the vicinity of the work crew. The system is portable, operating on rechargeable batteries or solar power, and can include multiple warning devices for alerting two or more work crews in a construction zone which has multiple active railway tracks therein. Welte et al, U.S. Pat. No. 5,907,294 teaches an early warning system for warning persons near a track work site of approaching trains using an ultrasonic sensor to detect vibrations on the running rail. The ultrasonic sensor must be in contact with the running rail and detects any form of vibration on the running rail, but such vibration detection is not determinative of the direction of actual train movement. Such means of detection is unreliable because it is susceptible to being activated when the train movement causing vibration is taking place on an adjacent track. Further, the use of an ultrasonic sensor to detect rail vibration is not capable of detecting train speed or direction since the ultrasonic sensor is either pointed directly at the rail or is touching the rail. These aforementioned warning systems do not give early warning to the train operator or to workers on the track.